Refactor (WIP) the event fetch pipeline

items_2/src/streams.rs

@@ -0,0 +1,77 @@
+use crate::WithLen;
+use err::Error;
+use serde::Serialize;
+use std::any::Any;
+
+pub trait CollectorType: Send + Unpin + WithLen {
+    type Input: Collectable;
+    type Output: ToJsonResult + Serialize;
+
+    fn ingest(&mut self, src: &mut Self::Input);
+    fn set_range_complete(&mut self);
+    fn set_timed_out(&mut self);
+    fn result(&mut self) -> Result<Self::Output, Error>;
+}
+
+pub trait Collector: Send + Unpin + WithLen {
+    fn ingest(&mut self, src: &mut dyn Collectable);
+    fn set_range_complete(&mut self);
+    fn set_timed_out(&mut self);
+    fn result(&mut self) -> Result<Box<dyn ToJsonResult>, Error>;
+}
+
+pub trait CollectableType {
+    type Collector: CollectorType<Input = Self>;
+
+    fn new_collector() -> Self::Collector;
+}
+
+pub trait Collectable: Any {
+    fn new_collector(&self) -> Box<dyn Collector>;
+    fn as_any_mut(&mut self) -> &mut dyn Any;
+}
+
+impl<T: CollectorType + 'static> Collector for T {
+    fn ingest(&mut self, src: &mut dyn Collectable) {
+        let src: &mut <T as CollectorType>::Input = src.as_any_mut().downcast_mut().expect("can not downcast");
+        T::ingest(self, src)
+    }
+
+    fn set_range_complete(&mut self) {
+        T::set_range_complete(self)
+    }
+
+    fn set_timed_out(&mut self) {
+        T::set_timed_out(self)
+    }
+
+    fn result(&mut self) -> Result<Box<dyn ToJsonResult>, Error> {
+        let ret = T::result(self)?;
+        Ok(Box::new(ret) as _)
+    }
+}
+
+impl<T: CollectableType + 'static> Collectable for T {
+    fn new_collector(&self) -> Box<dyn Collector> {
+        Box::new(T::new_collector()) as _
+    }
+
+    fn as_any_mut(&mut self) -> &mut dyn Any {
+        // TODO interesting: why exactly does returning `&mut self` not work here?
+        self
+    }
+}
+
+pub trait ToJsonBytes {
+    fn to_json_bytes(&self) -> Result<Vec<u8>, Error>;
+}
+
+pub trait ToJsonResult {
+    fn to_json_result(&self) -> Result<Box<dyn ToJsonBytes>, Error>;
+}
+
+impl ToJsonBytes for serde_json::Value {
+    fn to_json_bytes(&self) -> Result<Vec<u8>, Error> {
+        Ok(serde_json::to_vec(self)?)
+    }
+}